1. Field of the Invention
The present invention relates to an apparatus for recording and reproducing a video signal and an audio signal, and which, for example, is suitable for use in an 8 mm video tap recorder.
2. Description of the Prior Art
Standardization of a so-called 8 mm video tape recorder has been proposed. According to such standardization represented generally in U.S. Pat. No. 4,551,771 having a common assignee herewith, and as shown in FIG. 1 hereof, the recording and/or reproducing of a video signal on and/or from magnetic tape TP is carried out by first and second rotary magnetic heads H1 and H2 which are mounted on a rotary tape guide drum RD at respective locations having an angular spacing of 180.degree. therebetween. The magnetic tape TP is helically wrapped around the periphery of the tape guide drum over an angular range of 221.degree. by guide pins G1 and G2 and is normally transported longitudinally in the direction of the arrow t. In an interval of 180.degree. within the tape wrapping angle of 221.degree., the video signal is normally recorded on and/or reproduced from the magnetic tape TP by heads H1 and H2 alternately while rotating in the direction of the arrow d. In the remaining interval of 36.degree. within the tape wrapping angle, an audio signal, which is pulse-code-modulated (PCM) and time-base-compressed, is recorded on and/or reproduced from the magnetic tape TP by the same rotary heads H1 and H2.
The azimuth angles of the head gaps of the first and second rotary heads H1 and H2 are made different from each other in a range of .+-.10.degree.. In the proximity of the second rotary head H2, there is provided an auxiliary rotary magnetic head H3 which is used for playback when the tape speed is other than the standard tape speed for recording. The auxiliary head H3 is desirably spaced apart from the second rotary head H2 in the circumferential direction by a distance corresponding to two horizontal periods on magnetic tape TP. The rotary head H3 is shown to precede the head H2 with reference to the direction of rotation d. The azimuth of the head gap of auxiliary rotary magnetic head H3 is selected to be the same as the azimuth of the head gap of the first rotary magnetic head H1. Further, an erasing rotary magnetic head He is mounted on rotary drum RD at a location spaced angularly by 90.degree. relative to first and second rotary magnetic heads H1 and H2. The gap width of this erasing rotary head He corresponds to the combined width of two slant or skewed recording tracks.
As shown on FIG. 2, a video signal and a PCM (pulse-code-modulated) audio signal are recorded on tape TP in each of a succession of slant or skewed tracks T1,T2,T3, T4, . . . , each having a length corresponding to the wrapping angle of 221.degree., and which are formed by the first and second rotary heads H1 and H2, alternately. More particularly, in an overscan section or area AP of each of the skewed tracks T1,T2, . . . , having a length corresponding to an angular range of 36.degree. starting from the point where the respective rotary head H1 or H2 starts scanning the track, there is recorded the PCM audio signal corresponding to one field period of the video signal, but with the time base of such audio signal being compressed. In the succeeding area AV of the track having a length corresponding to an angular range of 180.degree., there is recorded by the head H1 or H2 a color video signal of one field period. Finally, at the trailing end portion or area AV of each track having a length corresponding to an angular range of 5.degree., there is provided a separating portion SP.
A rotary transformer apparatus (not shown) is employed for transmitting signals to and from rotary heads H1,H2,H3 and He. When a PCM audio signal is recorded in the so-called "after-recording mode", that is, when a new PCM audio signal is recorded in areas AP of skewed tracks on which a PCM audio signal has been previously recorded, the video signal recorded previously in the area AV of one of the skewed tracks is normally reproduced while the area AP is being erased by the erase rotary head He, and then the new PCM audio signal is recorded by the first and second rotary heads H1 and H2. This causes the following problems:
In that phase of the after-recording operation in which the erase rotary head He erases the areas AP of, for example, skewed tracks T1 and T2 in FIG. 2 and the second rotary head H2 simultaneously reproduces the video signal recorded in the area AV of skewed track T2, the erasing signal from the erase rotary head He is mixed directly, or through leakage in the rotary transformer, with the signal reproduced by rotary head H2 over a period corresponding to a 30.degree. rotation angle of the rotary head so that the reproduced synchronizing signal and video signal are disturbed considerably. As a result thereof, and as shown in FIG. 3, a noise bar a, which is a disturbed color picture in the lateral direction, appears in the portion of the reproduced picture slightly above the center thereof and the AFC (automatic frequency control) of the television receiver is disturbed considerably by the deteriorated signal.
Further along in the after-recording operation, while the new PCM audio signal is being sequentially recorded in the areas AP of skewed tracks T1 and T2 by the first and second rotary heads H1 and H2, such new PCM audio signal is mixed into the video signals reproduced by rotary heads H2 and H1, respectively, from the areas AV over a period corresponding to a 30.degree. rotation angle of the rotary head. Therefore, the synchronizing signal and the video signal are again disturbed considerably, and, in this case, as shown in FIG. 3, a noise bar b of a disturbed color picture in the lateral direction is produced in the lower portion of the reproduced picture and hence the AFC of the television receiver is greatly disturbed.